Optical scanning device, driving method of optical scanning device, and image drawing system

ABSTRACT

A driving controller provides a first driving signal having a first driving frequency to a first actuator, provides a second driving signal having a second driving frequency to a second actuator, derives a first average phase delay time by averaging a first phase delay time of an output signal of a first angle detection sensor with respect to the first driving signal in a plurality of cycles, derives a second average phase delay time by averaging a second phase delay time of an output signal of a second angle detection sensor with respect to the second driving signal in a plurality of cycles, generates a first reference signal based on the first driving signal and the first average phase delay time, and generates a second reference signal based on the second driving signal and the second average phase delay time.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 toJapanese Patent Application No. 2021-092417 filed on Jun. 1, 2021. Theabove application is hereby expressly incorporated by reference, in itsentirety, into the present application.

BACKGROUND 1. Technical Field

The present disclosure relates to an optical scanning device, a drivingmethod of an optical scanning device, and an image drawing system.

2. Description of the Related Art

A micromirror device (also referred to as a microscanner) is known asone of micro electro mechanical systems (MEMS) devices manufacturedusing the silicon (Si) microfabrication technique. An optical scanningdevice comprising the micromirror device is small and has low powerconsumption. Thus, applications in image drawing systems such as laserdisplays or laser projectors are expected.

In the micromirror device, a mirror portion is formed to be capable ofswinging around a first axis and a second axis that are orthogonal toeach other, and light reflected by the mirror portion istwo-dimensionally scanned by the swing of the mirror portion around eachaxis. In addition, a micromirror device that enables Lissajous scanningof light by causing a mirror portion to resonate around each axis hasbeen known.

JP2018-101040A discloses an optical scanning device including a sensorthat detects a rotation angle of a mirror portion, and a look-up tablein which a correction amount that is used for correcting an amplitudeand a phase of the rotation angle of the mirror portion obtained fromthe sensor and corresponds to each temperature is stored.

JP2017-181951A discloses an optical scanning device that detects acurrent generated by a change in capacitance of an actuator which drivesa mirror portion, outputs a current signal obtained by cutting acomponent of a predetermined frequency or higher, and adjusts a drivingsignal provided to the actuator based on a difference in time between amaximal value and a minimal value of the current signal.

JP2013-513828A discloses an optical scanning device that adjusts firstand second control frequencies in accordance with a phase of vibrationof a mirror portion so that a maximum amplitude of the vibration fallswithin a resonance range of the mirror portion, in which the first andsecond control frequencies substantially do not have a fixed integerratio.

SUMMARY

In the optical scanning device, a first angle detection sensor thatdetects an angle of the mirror portion around the first axis, and asecond angle detection sensor that detects the angle of the mirrorportion around the second axis are used. For example, the opticalscanning device outputs a reference signal (for example, a zero crosssignal) representing that the angle of the mirror portion is equal to areference angle, based on output signals of the first angle detectionsensor and the second angle detection sensor. The reference signal isused for controlling an irradiation timing of light by a light sourcethat irradiates the mirror portion with light.

The output signal of the first angle detection sensor may have anunstable signal waveform by receiving an influence of the swinging orthe like of the mirror portion around the second axis. Similarly, theoutput signal of the second angle detection sensor may have an unstablesignal waveform by receiving an influence of the swinging or the like ofthe mirror portion around the first axis. In these cases, in a casewhere the reference signal is output based on the output signals of thefirst angle detection sensor and the second angle detection sensor, anoutput timing of the reference signal is shifted depending on a cycle.In this case, the irradiation timing of light by the light source isshifted for each cycle, and image quality of a drawn image is decreased.

However, in the techniques disclosed in JP2018-101040A, JP2017-181951A,and JP2013-513828A, the shifting of the output timing of the referencesignal is not considered.

The present disclosure is conceived in view of the above matter, and anobject thereof is to provide an optical scanning device, a drivingmethod of an optical scanning device, and an image drawing system thatcan suppress a decrease in image quality of a drawn image.

An optical scanning device according to an aspect of the presentdisclosure comprises a mirror portion that has a reflecting surface onwhich an incidence ray is reflected, a first actuator that causes themirror portion to swing around a first axis which is in a planeincluding the reflecting surface at a time of a standstill of the mirrorportion, a second actuator that causes the mirror portion to swingaround a second axis which is in the plane including the reflectingsurface at the time of the standstill of the mirror portion andintersects with the first axis, a first angle detection sensor thatoutputs a signal corresponding to an angle of the mirror portion aroundthe first axis, a second angle detection sensor that outputs a signalcorresponding to an angle of the mirror portion around the second axis,and at least one processor, in which the processor is configured toprovide a first driving signal having a first driving frequency to thefirst actuator, provide a second driving signal having a second drivingfrequency to the second actuator, derive a first average phase delaytime by averaging a first phase delay time of the output signal of thefirst angle detection sensor with respect to the first driving signal ina plurality of cycles, derive a second average phase delay time byaveraging a second phase delay time of the output signal of the secondangle detection sensor with respect to the second driving signal in aplurality of cycles, generate a first reference signal representing thatthe angle around the first axis is equal to a reference angle based onthe first driving signal and the first average phase delay time, andgenerate a second reference signal representing that the angle aroundthe second axis is equal to a reference angle based on the seconddriving signal and the second average phase delay time.

In the optical scanning device according to the aspect of the presentdisclosure, the first angle detection sensor may include a pair of angledetection sensors arranged at positions that face each other with thefirst axis or the second axis interposed between the positions, theoutput signal of the first angle detection sensor may be an outputsignal obtained by adding or subtracting a pair of output signals outputfrom the pair of angle detection sensors, the second angle detectionsensor may include a pair of angle detection sensors arranged atpositions that face each other with the first axis or the second axisinterposed between the positions, and the output signal of the secondangle detection sensor may be an output signal obtained by adding orsubtracting a pair of output signals output from the pair of angledetection sensors.

In addition, in the optical scanning device according to the aspect ofthe present disclosure, the first reference signal may be a signalrepresenting that the angle around the first axis is zero, and thesecond reference signal may be a signal representing that the anglearound the second axis is zero.

In addition, in the optical scanning device according to the aspect ofthe present disclosure, the processor may be configured to derive thefirst average phase delay time by averaging the first phase delay timeat a point in time when the output signal of the first angle detectionsensor is zero, and derive the second average phase delay time byaveraging the second phase delay time at a point in time when the outputsignal of the second angle detection sensor is zero.

In addition, in the optical scanning device according to the aspect ofthe present disclosure, the processor may be configured to derive thefirst average phase delay time by averaging the first phase delay timefrom a point in time when the first driving signal is zero to the pointin time when the output signal of the first angle detection sensor iszero in a corresponding cycle, and derive the second average phase delaytime by averaging the second phase delay time from a point in time whenthe second driving signal is zero to the point in time when the outputsignal of the second angle detection sensor is zero in a correspondingcycle.

In addition, in the optical scanning device according to the aspect ofthe present disclosure, the processor may be configured to generate eachof the first reference signal and the second reference signal based on atime obtained by adding a shift time corresponding to a preset conditionto each of the first average phase delay time and the second averagephase delay time.

In addition, in the optical scanning device according to the aspect ofthe present disclosure, the condition may include the first phase delaytime and the second phase delay time.

In addition, in the optical scanning device according to the aspect ofthe present disclosure, the condition may further include a drivingvoltage of the first driving signal and a driving voltage of the seconddriving signal.

In addition, in the optical scanning device according to the aspect ofthe present disclosure, the condition may further include the firstdriving frequency and the second driving frequency.

In addition, in the optical scanning device according to the aspect ofthe present disclosure, the condition may further include an ambienttemperature.

In addition, in the optical scanning device according to the aspect ofthe present disclosure, a shift time derivation mode in which the shifttime is derived may be provided, and the processor may be configured toacquire the shift time by executing the shift time derivation mode incalibration, and use the shift time acquired in advance in thecalibration in generating the first reference signal and the secondreference signal.

In addition, in the optical scanning device according to the aspect ofthe present disclosure, an average phase delay time derivation mode inwhich the first average phase delay time and the second average phasedelay time are derived may be provided, and the processor may beconfigured to acquire the first average phase delay time and the secondaverage phase delay time by executing the average phase delay timederivation mode in calibration, and use the first average phase delaytime and the second average phase delay time acquired in advance in thecalibration in generating the first reference signal and the secondreference signal.

In addition, an image drawing system according to another aspect of thepresent disclosure is an image drawing system comprising above anyoptical scanning device, and a light source that irradiates the mirrorportion with light, in which the processor is configured to control anirradiation timing of the light of the light source based on the firstreference signal and the second reference signal.

In addition, a driving method of an optical scanning device according tostill another aspect of the present disclosure is a driving method of anoptical scanning device including a mirror portion that has a reflectingsurface on which an incidence ray is reflected, a first actuator thatcauses the mirror portion to swing around a first axis which is in aplane including the reflecting surface at a time of a standstill of themirror portion, a second actuator that causes the mirror portion toswing around a second axis which is in the plane including thereflecting surface at the time of the standstill of the mirror portionand intersects with the first axis, a first angle detection sensor thatoutputs a signal corresponding to an angle of the mirror portion aroundthe first axis, and a second angle detection sensor that outputs asignal corresponding to an angle of the mirror portion around the secondaxis, the driving method comprising providing a first driving signalhaving a first driving frequency to the first actuator, providing asecond driving signal having a second driving frequency to the secondactuator, deriving a first average phase delay time by averaging a firstphase delay time of the output signal of the first angle detectionsensor with respect to the first driving signal in a plurality ofcycles, deriving a second average phase delay time by averaging a secondphase delay time of the output signal of the second angle detectionsensor with respect to the second driving signal in a plurality ofcycles, generating a first reference signal representing that the anglearound the first axis is equal to a reference angle based on the firstdriving signal and the first average phase delay time, and generating asecond reference signal representing that the angle around the secondaxis is equal to a reference angle based on the second driving signaland the second average phase delay time.

According to the present disclosure, a decrease in image quality of adrawn image can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an image drawing system.

FIG. 2 is an external perspective view of a micromirror device.

FIG. 3 is a graph showing an example of a first driving signal.

FIG. 4 is a graph showing an example of a second driving signal.

FIG. 5 is a block diagram showing an example of a functionalconfiguration of a driving controller.

FIG. 6 is a diagram showing an example of signals output from a pair offirst angle detection sensors.

FIG. 7 is a diagram showing an example of signals output from a pair ofsecond angle detection sensors.

FIG. 8 is a circuit diagram showing an example of a configuration of afirst signal processing portion.

FIG. 9 is a diagram showing an example of first signal processing.

FIG. 10 is a diagram showing an example of second signal processing.

FIG. 11 is a diagram for describing shifting of a zero cross timing of afirst angle detection signal.

FIG. 12 is a diagram for describing derivation processing of a firstaverage phase delay time.

FIG. 13 is a diagram for describing derivation processing of a secondaverage phase delay time.

FIG. 14 is a diagram showing an example of a relationship between thefirst average phase delay time and a first shift time.

FIG. 15 is a diagram showing an example of a relationship between thesecond average phase delay time and a second shift time.

FIG. 16 is a diagram for describing generation processing of a firstzero cross pulse.

FIG. 17 is a diagram for describing generation processing of a secondzero cross pulse.

FIG. 18 is a flowchart showing an example of first shift time derivationprocessing.

FIG. 19 is a flowchart showing an example of second shift timederivation processing.

FIG. 20 is a flowchart showing an example of first zero cross pulsegeneration processing.

FIG. 21 is a flowchart showing an example of second zero cross pulsegeneration processing.

FIG. 22 is a schematic plan view of the image drawing system incalibration.

FIG. 23 is a flowchart showing an example of first calibrationprocessing.

FIG. 24 is a diagram for describing the first calibration processing.

FIG. 25 is a diagram for describing the first calibration processing.

FIG. 26 is a flowchart showing an example of second calibrationprocessing.

FIG. 27 is a diagram for describing the second calibration processing.

FIG. 28 is a diagram for describing the second calibration processing.

FIG. 29 is a plan view of a micromirror device according to amodification example.

FIG. 30 is a circuit diagram showing a configuration of a first signalprocessing portion according to the modification example.

FIG. 31 is a diagram showing an example of a relationship between afirst driving frequency and the first shift time.

DETAILED DESCRIPTION

Hereinafter, an embodiment according to the technique of the presentdisclosure will be described in detail with reference to the drawings.

First, a configuration of an image drawing system 10 according to thepresent embodiment will be described with reference to FIG. 1 . As shownin FIG. 1 , the image drawing system 10 includes an optical scanningdevice 2 and a light source 3. The optical scanning device 2 includes amicromirror device (hereinafter, referred to as an “MMD”) 4 and adriving controller 5. The driving controller 5 is an example of aprocessor according to the embodiment of the technique of thedisclosure.

The image drawing system 10 draws an image by optically scanning asurface to be scanned 6 by reflecting a light beam L of irradiation fromthe light source 3 by the MMD 4 under control of the driving controller5. The surface to be scanned 6 is, for example, a screen for projectingthe image, or a retina of an eye of a person.

The image drawing system 10 is applied to, for example, a Lissajousscanning type laser display. Specifically, the image drawing system 10can be applied to a laser scanning display such as augmented reality(AR) glasses or virtual reality (VR) glasses.

The MMD 4 is a piezoelectric biaxial drive type micromirror devicecapable of causing a mirror portion 20 (see FIG. 2 ) to swing around afirst axis a₁ and a second axis a₂ orthogonal to the first axis a₁.Hereinafter, a direction parallel to the second axis a₂ will be referredto as an X direction, a direction parallel to the first axis a₁ will bereferred to as a Y direction, and a direction orthogonal to the firstaxis a₁ and the second axis a₂ will be referred to as a Z direction. Inthe present embodiment, while an example in which the first axis a₁ isorthogonal to (that is, perpendicularly intersects with) the second axisa₂ is shown, the first axis a₁ may intersect with the second axis a₂ atan angle other than 90°. Here, intersecting means being within aconstant angle range centered at 90 degrees including an allowableerror.

The light source 3 is a laser device that emits, for example, laserlight as the light beam L. For example, the light source 3 outputs laserlight of three colors of red (R), green (G), and blue (B). It ispreferable that the light source 3 perpendicularly irradiates areflecting surface 20A (see FIG. 2 ) comprised in the mirror portion 20with the light beam L in a state where the mirror portion 20 of the MMD4 is at a standstill. In a case where the reflecting surface 20A isperpendicularly irradiated with the light beam L from the light source3, the light source 3 may be an obstacle in the drawing by scanning thesurface to be scanned 6 with the light beam L. Thus, it is preferablethat the reflecting surface 20A is perpendicularly irradiated with thelight beam L emitted from the light source 3 by controlling the lightbeam L by an optical system. The optical system may include a lens ormay not include a lens. In addition, an angle at which the reflectingsurface 20A is irradiated with the light beam L emitted from the lightsource 3 is not limited to a perpendicular angle. The reflecting surface20A may be irradiated with the light beam L in an inclined manner.

The driving controller 5 outputs a driving signal to the light source 3and the MMD 4 based on optical scanning information. The light source 3generates the light beam L based on the input driving signal andirradiates the MMD 4 with the light beam L. The MMD 4 causes the mirrorportion 20 to swing around the first axis a₁ and the second axis a₂based on the input driving signal.

By causing the mirror portion 20 to resonate around each of the firstaxis a₁ and the second axis a₂ by the driving controller 5, the lightbeam L reflected by the mirror portion 20 is scanned onto the surface tobe scanned 6 such that the light beam L draws a Lissajous waveform. Thisoptical scanning method is called a Lissajous scanning method.

Next, a configuration of the MMD 4 according to the present embodimentwill be described with reference to FIG. 2 . As shown in FIG. 2 , theMMD 4 includes the mirror portion 20, a first support portion 21, afirst movable frame 22, a second support portion 23, a second movableframe 24, a connecting portion 25, and a fixed frame 26. The MMD 4 is aso-called MEMS scanner.

The mirror portion 20 has the reflecting surface 20A for reflecting anincidence ray. The reflecting surface 20A is provided on one surface ofthe mirror portion 20 and is formed with a metal thin film of, forexample, gold (Au), aluminum (Al), silver (Ag), or a silver alloy. Ashape of the reflecting surface 20A is, for example, a circular shapecentered at an intersection between the first axis a₁ and the secondaxis a₂.

The first axis a₁ and the second axis a₂ are present in a planeincluding the reflecting surface 20A at a time of a standstill when themirror portion 20 is at a standstill. A planar shape of the MMD 4 is arectangular shape and is axially symmetric with respect to the firstaxis a₁ and axially symmetric with respect to the second axis a₂.

The first support portion 21 is arranged outside the mirror portion 20at each of positions that face each other with the second axis a₂interposed therebetween. The first support portions 21 are connected tothe mirror portion 20 on the first axis a₁ and support the mirrorportion 20 to be capable of swinging around the first axis a₁. In thepresent embodiment, the first support portions 21 are torsion bars thatstretch along the first axis a₁.

The first movable frame 22 is a frame having a rectangular shapesurrounding the mirror portion 20 and is connected to the mirror portion20 through the first support portion 21 on the first axis a₁. Apiezoelectric element 30 is formed on the first movable frame 22 at eachof positions that face each other with the first axis a₁ interposedtherebetween. In such a manner, a pair of first actuators 31 areconfigured by forming two piezoelectric elements 30 on the first movableframe 22.

The pair of first actuators 31 are arranged at positions that face eachother with the first axis a₁ interposed therebetween. The firstactuators 31 cause the mirror portion 20 to swing around the first axisa₁ by applying rotational torque around the first axis a₁ to the mirrorportion 20.

The second support portion 23 is arranged outside the first movableframe 22 at each of positions with the first axis a₁ interposedtherebetween. The second support portions 23 are connected to the firstmovable frame 22 on the second axis a₂ and support the first movableframe 22 and the mirror portion 20 to be capable of swinging around thesecond axis a₂. In the present embodiment, the second support portions23 are torsion bars that stretch along the second axis a₂.

The second movable frame 24 is a frame having a rectangular shapesurrounding the first movable frame 22 and is connected to the firstmovable frame 22 through the second support portion 23 on the secondaxis a₂. The piezoelectric element 30 is formed on the second movableframe 24 at each of positions that face each other with the second axisa₂ interposed therebetween. In such a manner, a pair of second actuators32 are configured by forming two piezoelectric elements 30 on the secondmovable frame 24.

The pair of second actuators 32 are arranged at positions that face eachother with the second axis a₂ interposed therebetween. The secondactuators 32 cause the mirror portion 20 to swing around the second axisa₂ by applying rotational torque about the second axis a₂ to the mirrorportion 20 and the first movable frame 22.

The connecting portion 25 is arranged outside the second movable frame24 at each of positions with the first axis a₁ interposed therebetween.The connecting portions 25 are connected to the second movable frame 24on the second axis a₂.

The fixed frame 26 is a frame having a rectangular shape surrounding thesecond movable frame 24 and is connected to the second movable frame 24through the connecting portion 25 on the second axis a₂.

In addition, a pair of first angle detection sensors 11A and 11B areprovided in the first movable frame 22 near the first support portions21 at positions that face each other with the first axis a₁ interposedtherebetween. Each of the pair of first angle detection sensors 11A and11B is configured with a piezoelectric element. Each of the first angledetection sensors 11A and 11B outputs a signal by converting a forceapplied by deformation of the first support portion 21 accompanied byrotational movement of the mirror portion 20 around the first axis a₁into a voltage. That is, the first angle detection sensors 11A and 11Boutput signals corresponding to an angle of the mirror portion 20 aroundthe first axis a₁.

In addition, a pair of second angle detection sensors 12A and 12B areprovided in the second movable frame 24 near the second support portions23 at positions that face each other with the second axis a₂ interposedtherebetween. Each of the pair of second angle detection sensors 12A and12B is configured with a piezoelectric element. Each of the second angledetection sensors 12A and 12B outputs a signal by converting a forceapplied by deformation of the second support portion 23 accompanied byrotational movement of the mirror portion 20 around the second axis a₂into a voltage. That is, the second angle detection sensors 12A and 12Boutput signals corresponding to the angle of the mirror portion 20around the second axis a₂.

In FIG. 2 , wiring lines and electrode pads for providing drivingsignals to the first actuators 31 and the second actuators 32 are notshown. In addition, in FIG. 2 , wiring lines and electrode pads foroutputting signals from the first angle detection sensors 11A and 11Band the second angle detection sensors 12A and 12B are not shown. Aplurality of electrode pads are provided on the fixed frame 26.

A deflection angle (hereinafter, referred to as a “first deflectionangle”) θ₁ of the mirror portion 20 around the first axis a₁ iscontrolled by the driving signal (hereinafter, referred to as a “firstdriving signal”) provided to the first actuators 31 by the drivingcontroller 5. The first driving signal is, for example, a sinusoidalalternating current voltage. The first driving signal includes a drivingvoltage waveform V_(1A)(t) applied to one of the pair of first actuators31 and a driving voltage waveform V_(1B)(t) applied to the other. Thedriving voltage waveform V_(1A)(t) and the driving voltage waveformV_(1B)(t) are in anti-phase with each other (that is, have a phasedifference of 180°).

The first deflection angle θ₁ is an angle at which a line normal to thereflecting surface 20A is inclined with respect to the Z direction in anXZ plane.

A deflection angle (hereinafter, referred to as a “second deflectionangle”) θ₂ of the mirror portion 20 around the second axis a₂ iscontrolled by the driving signal (hereinafter, referred to as a “seconddriving signal”) provided to the second actuators 32 by the drivingcontroller 5. The second driving signal is, for example, a sinusoidalalternating current voltage. The second driving signal includes adriving voltage waveform V_(2A)(t) applied to one of the pair of secondactuators 32 and a driving voltage waveform V_(2B)(t) applied to theother. The driving voltage waveform V_(2A)(t) and the driving voltagewaveform V_(2B)(t) are in anti-phase with each other (that is, have aphase difference of 180°).

The second deflection angle θ₂ is an angle at which the line normal tothe reflecting surface 20A is inclined with respect to the Z directionin a YZ plane.

FIG. 3 shows an example of the first driving signal, and FIG. 4 shows anexample of the second driving signal. FIG. 3 shows the driving voltagewaveforms V_(1A)(t) and V_(1B)(t) included in the first driving signal.FIG. 4 shows the driving voltage waveforms V_(2A)(t) and V_(2B)(t)included in the second driving signal.

Each of the driving voltage waveforms V_(1A)(t) and V_(1B)(t) isrepresented as follows.

V _(1A)(t)=V _(off1) +V ₁ sin(2πf _(d1) t)

V _(1B)(t)=V _(off1) +V ₁ sin(2πf _(d1) t+α)

Here, V₁ is an amplitude voltage. V_(off1) is a bias voltage. V_(off1)may be zero. In addition, f_(d1) is a driving frequency (hereinafter,referred to as a “first driving frequency”). In addition, t is time. Inaddition, a is a phase difference between the driving voltage waveformsV_(1A)(t) and V_(1B)(t). In the present embodiment, for example, α=180°is assumed.

By applying the driving voltage waveforms V_(1A)(t) and V_(1B)(t) to thepair of first actuators 31, the mirror portion 20 swings around thefirst axis a₁ with the first driving frequency f_(d1).

Each of the driving voltage waveforms V_(2A)(t) and V_(2B)(t) isrepresented as follows.

V _(2A)(t)=V _(off2) +V ₂ sin(2πf _(d2) t+φ)

V _(2B)(t)=V _(off2) +V ₂ sin(2πf _(d2) t+β+φ)

Here, V₂ is an amplitude voltage. V_(off2) is a bias voltage. V_(off2)may be zero. In addition, f_(d2) is a driving frequency (hereinafter,referred to as a “second driving frequency”). In addition, t is time. Inaddition, β is a phase difference between the driving voltage waveformsV_(2A)(t) and V_(2B)(t). In the present embodiment, for example, β=180°is assumed. In addition, φ is a phase difference between the drivingvoltage waveforms V_(1A)(t) and V_(1B)(t) and the driving voltagewaveforms V_(2A)(t) and V_(2B)(t).

By applying the driving voltage waveforms V_(2A)(t) and V_(2B)(t) to thepair of second actuators 32, the mirror portion 20 swings around thesecond axis a₂ with the second driving frequency f_(d2).

The first driving frequency f_(d1) is set to match a resonance frequencyof the mirror portion 20 around the first axis a₁. The second drivingfrequency f_(d2) is set to match the resonance frequency of the mirrorportion 20 around the second axis a₂. In the present embodiment,f_(d1)>f_(d2) is assumed. That is, the mirror portion 20 has a higherswing frequency around the first axis a₁ than a swing frequency aroundthe second axis a₂. The first driving frequency f_(d1) and the seconddriving frequency f_(d2) may not necessarily match the resonancefrequency. For example, each of the first driving frequency f_(d1) andthe second driving frequency f_(d2) may be a frequency within afrequency range near the resonance frequency (for example, a half-widthrange of a frequency distribution having the resonance frequency as apeak value). For example, this frequency range is within a range of aso-called Q-value.

Next, a functional configuration of the driving controller 5 will bedescribed with reference to FIG. 5 . As shown in FIG. 5 , the drivingcontroller 5 includes a first driving signal generation portion 60A, asecond driving signal generation portion 60B, a first signal processingportion 61A, a second signal processing portion 61B, a first phase shiftportion 62A, a second phase shift portion 62B, a first derivationportion 63A, a second derivation portion 63B, a third derivation portion64, a first zero cross pulse output portion 65A, a second zero crosspulse output portion 65B, and a light source driving portion 66.

The first driving signal generation portion 60A, the first signalprocessing portion 61A, and the first phase shift portion 62A mayperform a feedback control to maintain a vibration state where the swingof the mirror portion 20 around the first axis a₁ has a designatedfrequency. The second driving signal generation portion 60B, the secondsignal processing portion 61B, and the second phase shift portion 62Bmay perform a feedback control to maintain a vibration state where theswing of the mirror portion 20 around the second axis a₂ has adesignated frequency.

The first driving signal generation portion 60A generates the firstdriving signal including the driving voltage waveforms V_(1A)(t) andV_(1B)(t) based on a reference waveform and provides the generated firstdriving signal to the pair of first actuators 31 through the first phaseshift portion 62A. Accordingly, the mirror portion 20 swings around thefirst axis a₁.

The second driving signal generation portion 60B generates the seconddriving signal including the driving voltage waveforms V_(2A)(t) andV_(2B)(t) based on the reference waveform and provides the generatedsecond driving signal to the pair of second actuators 32 through thesecond phase shift portion 62B. Accordingly, the mirror portion 20swings around the second axis a₂.

The first driving signal generated by the first driving signalgeneration portion 60A and the second driving signal generated by thesecond driving signal generation portion 60B are synchronized in phaseas shown by <p in the expression showing the driving voltage waveformsV_(2A)(t) and V_(2B)(t) included in the second driving signal.

The first angle detection sensors 11A and 11B output the signalscorresponding to the angle of the mirror portion 20 around the firstaxis a₁. The second angle detection sensors 12A and 12B output thesignals corresponding to the angle of the mirror portion 20 around thesecond axis a₂.

FIG. 6 shows an example of the signals output from the pair of firstangle detection sensors 11A and 11B. In FIG. 6 , S1 a ₁ and S1 a ₂represent the signals output from the pair of first angle detectionsensors 11A and 11B in a case where the mirror portion 20 is caused toswing around only the first axis a₁ and not swing around the second axisa₂. The signals S1 a ₁ and S1 a ₂ are waveform signals similar to asinusoidal wave having the first driving frequency f_(d1) and are inanti-phase with each other.

In a case where the mirror portion 20 is caused to swing around thefirst axis a₁ and the second axis a₂ at the same time, a vibration noiseRN1 caused by the swing of the mirror portion 20 around the second axisa₂ is superimposed on the output signals of the pair of first angledetection sensors 11A and 11B. S1 b ₁ represents a signal after thevibration noise RN1 is superimposed on the signal S1 a ₁. S1 b ₂represents a signal after the vibration noise RN1 is superimposed on thesignal S1 a ₂. In the example in FIG. 6 , the vibration noise RN1 isshown in a highlighted manner for description of the present embodiment.

FIG. 7 shows an example of the signals output from the pair of secondangle detection sensors 12A and 12B. In FIG. 7 , S2 a ₁ and S2 a ₂represent the signals output from the pair of second angle detectionsensors 12A and 12B in a case where the mirror portion 20 is caused toswing around only the second axis a₂ and not swing around the first axisa₁. The signals S2 a ₁ and S2 a 2 are waveform signals similar to asinusoidal wave having the second driving frequency f_(d2) and are inanti-phase with each other.

In a case where the mirror portion 20 is caused to swing around thefirst axis a₁ and the second axis a₂ at the same time, a vibration noiseRN2 caused by the swing of the mirror portion 20 around the first axisa₁ is superimposed on the output signals of the pair of second angledetection sensors 12A and 12B. S2 b ₁ represents a signal obtained bythe superimposition of the vibration noise RN2 on the signal S2 a ₁. S2b ₂ represents a signal obtained by the superimposition of the vibrationnoise RN2 on the signal S2 a ₂. In the example in FIG. 7 , the vibrationnoise RN2 is shown in a highlighted manner for description of thepresent embodiment.

The first signal processing portion 61A generates a signal (hereinafter,referred to as a “first angle detection signal”) S1 c obtained byremoving the vibration noise RN1 based on S1 a ₁ and S1 a ₂ output fromthe pair of first angle detection sensors 11A and 11B. The second signalprocessing portion 61B generates a signal (hereinafter, referred to as a“second angle detection signal”) S2 c obtained by removing the vibrationnoise RN2 based on S2 a ₁ and S2 a ₂ output from the pair of secondangle detection sensors 12A and 12B.

The first signal processing portion 61A can be implemented by, forexample, a circuit having a configuration shown in FIG. 8 as an example.As shown in FIG. 8 , the first signal processing portion 61A isconfigured with a buffer amplifier 71, a variable gain amplifier 72, asubtraction circuit 73, and a gain adjustment circuit 74. The gainadjustment circuit 74 is configured with a first band pass filter (BPF)circuit 75A, a second BPF circuit 75B, a first wave detection circuit76A, a second wave detection circuit 76B, and a subtraction circuit 77.

The subtraction circuit 73 and the subtraction circuit 77 aredifferential amplification circuits configured with operationalamplifiers.

The signal S1 b ₁ output from the first angle detection sensor 11A isinput into a positive input terminal (non-inverting input terminal) ofthe subtraction circuit 73 through the buffer amplifier 71. In addition,a signal output from the buffer amplifier 71 branches in the middle ofbeing input into the subtraction circuit 73 and is input into the firstBPF circuit 75A in the gain adjustment circuit 74.

The signal S1 b ₂ output from the first angle detection sensor 11B isinput into a negative input terminal (inverting input terminal) of thesubtraction circuit 73 through the variable gain amplifier 72. Inaddition, a signal output from the variable gain amplifier 72 branchesin the middle of being input into the subtraction circuit 73 and isinput into the second BPF circuit 75B in the gain adjustment circuit 74.

Each of the first BPF circuit 75A and the second BPF circuit 75B has apassband B1 having the second driving frequency f_(d2) as a centerfrequency. For example, the passband B1 is a frequency band of f_(d2)±5kH. The vibration noise RN1 has the second driving frequency f_(d2) andthus, passes through the passband B1. Accordingly, the first BPF circuit75A extracts the vibration noise RN1 from the signal input from thebuffer amplifier 71 and outputs the vibration noise RN1. The second BPFcircuit 75B extracts the vibration noise RN1 from the signal input fromthe variable gain amplifier 72 and outputs the vibration noise RN1.

Each of the first wave detection circuit 76A and the second wavedetection circuit 76B is configured with, for example, a root meansquared value to direct current converter (RMS-DC converter). The firstwave detection circuit 76A converts an amplitude of the vibration noiseRN1 input from the first BPF circuit 75A into a DC voltage signal andinputs the DC voltage signal into a positive input terminal of thesubtraction circuit 77. The second wave detection circuit 76B convertsthe amplitude of the vibration noise RN1 input from the second BPFcircuit 75B into a DC voltage signal and inputs the DC voltage signalinto a negative input terminal of the subtraction circuit 77.

The subtraction circuit 77 outputs a value d₁ obtained by subtractingthe DC voltage signal input from the second wave detection circuit 76Bfrom the DC voltage signal input from the first wave detection circuit76A. The value d₁ corresponds to a difference between the amplitude ofthe vibration noise RN1 included in the signal S1 b ₁ output from thefirst angle detection sensor 11A and the amplitude of the vibrationnoise RN1 included in the signal S1 b ₂ output from the first angledetection sensor 11B. The subtraction circuit 77 inputs the value d₁into a gain adjustment terminal of the variable gain amplifier 72 as again adjustment value.

The variable gain amplifier 72 adjusts an amplitude level of the signalS1 b ₂ by multiplying the signal S1 b ₂ input from the first angledetection sensor 11B by the value d₁ input as the gain adjustment value.In such a manner, by performing a feedback control by the gainadjustment circuit 74, the amplitude of the vibration noise RN1 includedin the signal S1 b ₂ after passing through the variable gain amplifier72 is adjusted to match the amplitude of the vibration noise RN1included in the signal S1 b ₁ after passing through the buffer amplifier71.

The subtraction circuit 73 outputs a value obtained by subtracting thesignal S1 b ₂ input to the negative input terminal from the signal S1 b₁ input to the positive input terminal. Since the amplitudes of thevibration noises RN1 included in both signals are matched by thefeedback control, the vibration noises RN1 included in both signals areoffset by subtraction processing performed by the subtraction circuit73. Accordingly, the first angle detection signal S1 c (see FIG. 9 )that is a signal obtained by removing the vibration noise RN1 is outputfrom the subtraction circuit 73.

FIG. 9 shows a state where the first angle detection signal S1 c isgenerated based on S1 b ₁ and S1 b ₂ output from the pair of first angledetection sensors 11A and 11B. The first angle detection signal S1 ccorresponds to a signal obtained by doubling an amplitude of the signalobtained by removing the vibration noise RN1 from the signal S1 b ₁.

In a case where the swing of the mirror portion 20 around the first axisa₁ maintains a resonance state, the first angle detection signal S1 coutput from the first signal processing portion 61A has a delay of 90°in phase with respect to the driving voltage waveform V_(1A)(t) includedin the first driving signal as shown in FIG. 9 .

The second signal processing portion 61B can be implemented by the sameconfiguration as the first signal processing portion 61A and thus, willnot be described.

FIG. 10 shows a state where the second angle detection signal S2 c isgenerated based on S2 b ₁ and S2 b ₂ output from the pair of secondangle detection sensors 12A and 12B. The second angle detection signalS2 c corresponds to a signal obtained by doubling an amplitude of thesignal obtained by removing the vibration noise RN2 from the signal S2 b₁.

In a case where the swing of the mirror portion 20 around the secondaxis a₂ maintains a resonance state, the second angle detection signalS2 c output from the second signal processing portion 61B has a delay of90° in phase with respect to the driving voltage waveform V_(2A)(t)included in the second driving signal as shown in FIG. 10 .

The first angle detection signal S1 c generated by the first signalprocessing portion 61A is fed back to the first driving signalgeneration portion 60A. The first phase shift portion 62A shifts phasesof the driving voltage waveforms output from the first driving signalgeneration portion 60A. For example, the first phase shift portion 62Ashifts the phases by 90°.

The second angle detection signal S2 c generated by the second signalprocessing portion 61B is fed back to the second driving signalgeneration portion 60B. The second phase shift portion 62B shifts phasesof the driving voltage waveforms output from the second driving signalgeneration portion 60B. For example, the second phase shift portion 62Bshifts the phases by 90°.

The first angle detection signal S1 c generated by the first signalprocessing portion 61A is ideally a sinusoidal wave but generally not asmooth sinusoidal wave. This is because an influence of the swing of themirror portion 20 around the second axis a₂ cannot be removed inprocessing performed by the first signal processing portion 61A. In thiscase, as shown in FIG. 11 as an example, a zero cross timing of thefirst angle detection signal S1 c is slightly shifted depending on acycle. In FIG. 11 , an example in which waveforms of the zero crosstiming of first angle detection signal S1 c in a plurality of cycles aresuperimposed is shown.

Therefore, the first derivation portion 63A reduces an influence of theshift for each cycle by averaging the first angle detection signal S1 cin the plurality of cycles. Hereinafter, processing performed by thefirst derivation portion 63A will be described.

The first derivation portion 63A derives a first average phase delaytime by averaging a phase delay time (hereinafter, referred to as a“first phase delay time”) of the first angle detection signal S1 c withrespect to the first driving signal in the most recent plurality ofcycles. Specifically, as shown in FIG. 12 as an example, for the firstdriving signal and the first angle detection signal S1 c in the mostrecent plurality of cycles, the first derivation portion 63A derives thefirst average phase delay time by averaging a first phase delay time t1from a point in time when the first driving signal is zero to a point intime when the first angle detection signal S1 c is zero in acorresponding cycle. In the present embodiment, the first driving signalis offset by an amount corresponding to the bias voltage V_(off1). Thus,the point in time when the first driving signal is zero means a point intime when the first driving signal is V_(off1).

Similarly, the second angle detection signal S2 c generated by thesecond signal processing portion 61B is also ideally a sinusoidal wavebut generally not a smooth sinusoidal wave because an influence of theswing of the mirror portion 20 around the first axis a₁ remains.Therefore, the second derivation portion 63B reduces the influence ofthe shift for each cycle by averaging the second angle detection signalS2 c in the plurality of cycles. Hereinafter, processing performed bythe second derivation portion 63B will be described.

The second derivation portion 63B derives a second average phase delaytime by averaging a phase delay time (hereinafter, referred to as a“second phase delay time”) of the second angle detection signal S2 cwith respect to the second driving signal in the most recent pluralityof cycles. Specifically, as shown in FIG. 13 as an example, for thesecond driving signal and the second angle detection signal S2 c in themost recent plurality of cycles, the second derivation portion 63Bderives the second average phase delay time by averaging a second phasedelay time t2 from a point in time when the second driving signal iszero to a point in time when the second angle detection signal S2 c iszero in a corresponding cycle. In the present embodiment, the seconddriving signal is offset by an amount corresponding to the bias voltageV_(off2). Thus, the point in time when the second driving signal is zeromeans a point in time when the second driving signal is V_(off2).

In the above processing performed by the first derivation portion 63Aand the second derivation portion 63B, while the point in time when thesinusoidal wave becomes zero from a negative value toward a positivevalue is used, the present disclosure is not limited thereto. Forexample, a point in time when the sinusoidal wave becomes zero from apositive value toward a negative value may be used, or both of the pointin time when the sinusoidal wave becomes zero from a negative valuetoward a positive value and the point in time when the sinusoidal wavebecomes zero from a positive value toward a negative value may be used.

By the above processing performed by the first derivation portion 63Aand the second derivation portion 63B, an influence of a difference inzero cross timing of the first angle detection signal S1 c and thesecond angle detection signal S2 c between each cycle can be reduced.However, a shift having a shift time t3 ₁ (hereinafter, referred to asthe “first shift time t3 ₁”) may occur between a timing at which thefirst angle detection signal S1 c becomes zero and an actual timing atwhich the first deflection angle θ₁ becomes zero. Similarly, a shifthaving a shift time t3 ₂ (hereinafter, referred to as the “second shifttime t3 ₂”) may occur between a timing at which the second angledetection signal S2 c becomes zero and an actual timing at which thesecond deflection angle θ₂ becomes zero.

FIG. 14 shows an example of a relationship between the first averagephase delay time and the first shift time t3 ₁, and FIG. 15 shows anexample of a relationship between the second average phase delay timeand the second shift time t3 ₂. As shown in FIG. 14 , as the firstaverage phase delay time is increased, the first shift time t3 ₁ isincreased. As shown in FIG. 15 , as the second average phase delay timeis increased, the second shift time t3 ₂ is decreased.

Therefore, the third derivation portion 64 derives the first shift timet3 ₁ and the second shift time t3 ₂ as shift times corresponding to apreset condition. In the present embodiment, an example of applying thefirst average phase delay time and the second average phase delay timeas this condition will be described. Instead of the first average phasedelay time, for example, the first phase delay time in the most recentcycle may be used. In addition, instead of the second average phasedelay time, for example, the second phase delay time in the most recentcycle may be used.

Specifically, the third derivation portion 64 derives the first shifttime t3 ₁ corresponding to a first average phase delay time t1 _(avg) inaccordance with the following function f1.

t3₁ =f1(t1_(avg))

Instead of the function f1, the third derivation portion 64 may derivethe first shift time t3 ₁ corresponding to the first average phase delaytime t1 _(avg) using a look-up table in which the first average phasedelay time t1 _(avg) is associated with the first shift time t3 ₁.

In addition, the third derivation portion 64 derives the second shifttime t3 ₂ corresponding to a second average phase delay time t2 _(avg)in accordance with the following function f2.

t3₂ =f2(t2_(avg))

Instead of the function f2, the third derivation portion 64 may derivethe second shift time t3 ₂ corresponding to the second average phasedelay time t2 _(avg) using a look-up table in which the second averagephase delay time t2 _(avg) is associated with the second shift time t3₂.

The function f1 is a function obtained by calibration and is obtained byapproximating a relationship between the first average phase delay timeand the first shift time t3 ₁. The function f2 is a function obtained bycalibration and is obtained by approximating a relationship between thesecond average phase delay time and the second shift time t3 ₂. Detailsof the calibration will be described later.

The first zero cross pulse output portion 65A generates a referencesignal (hereinafter, referred to as a “first reference signal”) based onthe first driving signal, the first average phase delay time derived bythe first derivation portion 63A, and the first shift time t3 ₁ derivedby the third derivation portion 64. The first reference signal is asignal representing that the angle of the mirror portion 20 around thefirst axis a₁ is equal to a reference angle. In the present embodiment,an example of applying zero as this reference angle will be described.That is, the first zero cross pulse output portion 65A generates a zerocross pulse (hereinafter, referred to as a “first zero cross pulse”) ZC1as an example of the first reference signal based on the first drivingsignal, the first average phase delay time derived by the firstderivation portion 63A, and the first shift time t3 ₁ derived by thethird derivation portion 64. The first zero cross pulse output portion65A is configured with a zero cross detection circuit. The first zerocross pulse is a zero cross signal representing that the angle of themirror portion 20 around the first axis a₁ is zero.

As shown in FIG. 16 , the first zero cross pulse output portion 65Agenerates the first zero cross pulse ZC1 at a timing after an elapse ofan added time of the first average phase delay time and the first shifttime t3 ₁ from a timing at which the first driving signal crosses zero(in the present embodiment, V_(off1)). The first zero cross pulse outputportion 65A outputs the generated first zero cross pulse ZC1 to thelight source driving portion 66.

The second zero cross pulse output portion 65B generates a referencesignal (hereinafter, referred to as a “second reference signal”) basedon the second driving signal, the second average phase delay timederived by the second derivation portion 63B, and the second shift timet3 ₂ derived by the third derivation portion 64. The second referencesignal is a signal representing that the angle of the mirror portion 20around the second axis a₂ is equal to a reference angle. In the presentembodiment, an example of applying zero as this reference angle will bedescribed. That is, the second zero cross pulse output portion 65Bgenerates a zero cross pulse (hereinafter, referred to as a “second zerocross pulse”) ZC2 as an example of the second reference signal based onthe second driving signal, the second average phase delay time derivedby the second derivation portion 63B, and the second shift time t3 ₂derived by the third derivation portion 64. The second zero cross pulseoutput portion 65B is configured with a zero cross detection circuit.The second zero cross pulse is a zero cross signal representing that theangle of the mirror portion 20 around the second axis a₂ is zero.

As shown in FIG. 17 , the second zero cross pulse output portion 65Bgenerates the second zero cross pulse ZC2 at a timing after an elapse ofan added time of the second average phase delay time and the secondshift time t3 ₂ from a timing at which the second driving signal crosseszero (in the present embodiment, V_(off2)). The second zero cross pulseoutput portion 65B outputs the generated second zero cross pulse ZC2 tothe light source driving portion 66.

While the first zero cross pulse output portion 65A and the second zerocross pulse output portion 65B output the zero cross pulses using bothof the point in time when the sinusoidal wave becomes zero from anegative value toward a positive value and the point in time when thesinusoidal wave becomes zero from a positive value toward a negativevalue, the present disclosure is not limited thereto. For example, thefirst zero cross pulse output portion 65A and the second zero crosspulse output portion 65B may output the zero cross pulses using any oneof the point in time when the sinusoidal wave becomes zero from anegative value toward a positive value or the point in time when thesinusoidal wave becomes zero from a positive value toward a negativevalue.

The light source driving portion 66 drives the light source 3 based on,for example, drawing data supplied from an outside of the image drawingsystem 10. In addition, the light source driving portion 66 controls anirradiation timing of the laser light by the light source 3 so that theirradiation timing is synchronized with the first zero cross pulse ZC1and the second zero cross pulse ZC2.

Next, a flow of first shift time derivation processing will be describedwith reference to FIG. 18 . For example, the first shift time derivationprocessing is executed at a predetermined time interval during thedrawing of the image by the image drawing system 10. This time intervalmay be, for example, a time interval corresponding to one cycle of thefirst driving signal, a time interval corresponding to a plurality ofcycles, or a preset time interval regardless of the cycle.

In step S10 in FIG. 18 , for each cycle, the first derivation portion63A acquires the first phase delay time from the point in time when thefirst driving signal is zero to the point in time when the first angledetection signal S1 c is zero in the corresponding cycle. In step S12,the first derivation portion 63A derives the first average phase delaytime by averaging the first phase delay time in the most recentplurality of cycles acquired in step S10.

In step S14, the third derivation portion 64 derives the first shifttime 31 corresponding to the first average phase delay time derived instep S12 in accordance with the function f1. In a case where theprocessing in step S14 is finished, the first shift time derivationprocessing is finished. The first average phase delay time and the firstshift time t3 ₁ are updated by periodically executing the first shifttime derivation processing during the drawing of the image.

Next, a flow of second shift time derivation processing will bedescribed with reference to FIG. 19 . For example, the second shift timederivation processing is executed at a predetermined time intervalduring the drawing of the image by the image drawing system 10. Thistime interval may be, for example, a time interval corresponding to onecycle of the second driving signal, a time interval corresponding to aplurality of cycles, or a preset time interval regardless of the cycle.

In step S20 in FIG. 19 , for each cycle, the second derivation portion63B acquires the second phase delay time from the point in time when thesecond driving signal is zero to the point in time when the second angledetection signal S2 c is zero in the corresponding cycle. In step S22,the second derivation portion 63B derives the second average phase delaytime by averaging the second phase delay time in the most recentplurality of cycles acquired in step S20.

In step S24, the third derivation portion 64 derives the second shifttime t3 ₂ corresponding to the second average phase delay time derivedin step S22 in accordance with the function f1. In a case where theprocessing in step S24 is finished, the second shift time derivationprocessing is finished. The second average phase delay time and thesecond shift time t3 ₂ are updated by periodically executing the secondshift time derivation processing during the drawing of the image.

Next, a flow of first zero cross pulse generation processing will bedescribed with reference to FIG. 20 . For example, the first zero crosspulse generation processing shown in FIG. 20 is executed during thedrawing of the image by the image drawing system 10.

In step S30 in FIG. 20 , the first zero cross pulse output portion 65Adetermines whether or not the first driving signal is zero. In a casewhere this determination results in a positive determination, theprocessing transitions to step S32. In a case where a negativedetermination is made, step S30 is executed again.

In step S32, the first zero cross pulse output portion 65A waits for theelapse of the added time of the first average phase delay time and thefirst shift time t3 ₁ derived by the first shift time derivationprocessing from the timing at which the first driving signal becomeszero in step S30. In a case where the added time of the first averagephase delay time and the first shift time t3 ₁ elapses from the timingat which the first driving signal becomes zero in step S30, thedetermination in step S32 results in a positive determination, and theprocessing transitions to step S34.

In step S34, the first zero cross pulse output portion 65A generates thefirst zero cross pulse ZC1 and outputs the generated first zero crosspulse ZC1 to the light source driving portion 66. In a case where theprocessing in step S34 is finished, the processing returns to step S30.In a case where drawing processing of the image by the image drawingsystem 10 is finished, the first zero cross pulse generation processingis finished.

Next, a flow of second zero cross pulse generation processing will bedescribed with reference to FIG. 21 . For example, the second zero crosspulse generation processing shown in FIG. 21 is executed during thedrawing of the image by the image drawing system 10.

In step S40 in FIG. 21 , the second zero cross pulse output portion 65Bdetermines whether or not the second driving signal is zero. In a casewhere this determination results in a positive determination, theprocessing transitions to step S42. In a case where a negativedetermination is made, step S40 is executed again.

In step S42, the second zero cross pulse output portion 65B waits forthe elapse of the added time of the second average phase delay time andthe second shift time t3 ₂ derived by the second shift time derivationprocessing from the timing at which the second driving signal becomeszero in step S40. In a case where the added time of the second averagephase delay time and the second shift time t3 ₂ elapses from the timingat which the second driving signal becomes zero in step S40, thedetermination in step S42 results in a positive determination, and theprocessing transitions to step S44.

In step S44, the second zero cross pulse output portion 65B generatesthe second zero cross pulse ZC2 and outputs the generated second zerocross pulse ZC2 to the light source driving portion 66. In a case wherethe processing in step S44 is finished, the processing returns to stepS40. In a case where the drawing processing of the image by the imagedrawing system 10 is finished, the second zero cross pulse generationprocessing is finished.

Next, processing of obtaining the functions f1 and f2 by the calibrationwill be described. FIG. 22 is a schematic plan view of the image drawingsystem 10 in the calibration. As shown in FIG. 22 , in the calibration,the image drawing system 10 further comprises an imaging apparatus 7.The imaging apparatus 7 is provided at a position at which the surfaceto be scanned 6 can be imaged. The imaging apparatus 7 images thesurface to be scanned 6 at a preset frame rate and outputs image dataobtained by the imaging to the driving controller 5. For example, theframe rate of the imaging apparatus 7 is set to the same frame rate as aframe rate at which the image drawing system 10 draws the image.Examples of the imaging apparatus 7 include a digital camera.

The optical scanning device 2 according to the present embodiment has ashift time derivation mode in which the first shift time t3 ₁ and thesecond shift time t3 ₂ are derived. First calibration processing shownin FIG. 23 and second calibration processing shown in FIG. 26 areexecuted by executing the shift time derivation mode in the calibration.Examples of an execution timing of the calibration include when theoptical scanning device 2 is started, and a timing at which aninstruction to execute the calibration is input by a user. In addition,the execution timing of the calibration may be before the opticalscanning device 2 is shipped from a factory. In this case, for example,data obtained by the calibration is stored in a non-volatile storageportion comprised in the driving controller 5. In addition, in thiscase, the imaging apparatus 7 may not be included in the image drawingsystem 10 in a user location that is a shipment destination of theoptical scanning device 2.

In step S50 in FIG. 23 , as described above, the first driving signalgeneration portion 60A generates the first driving signal and providesthe generated first driving signal to the pair of first actuators 31through the first phase shift portion 62A. That is, in the firstcalibration processing, the mirror portion 20 is caused to swing aroundonly the first axis a₁ and not swing around the second axis a₂.

In step S52, for each cycle, the first derivation portion 63A acquiresthe first phase delay time from the point in time when the first drivingsignal is zero to the point in time when the first angle detectionsignal S1 c is zero in the corresponding cycle. In step S54, the firstderivation portion 63A derives the first average phase delay time byaveraging the first phase delay time in the most recent plurality ofcycles acquired in step S52.

In step S56, the first zero cross pulse output portion 65A generates thefirst zero cross pulse ZC1 at the timing after the elapse of the addedtime of the first average phase delay time and the first shift time t3 ifrom the timing at which the first driving signal crosses zero. Thefirst zero cross pulse output portion 65A outputs the generated firstzero cross pulse ZC1 to the light source driving portion 66. In thefirst calibration processing, the light source driving portion 66performs irradiation with the laser light from the light source 3 insynchronization with the first zero cross pulse ZC1. At this point, thefirst shift time t3 i is a time set as a temporary value.

The above processing from step S50 to step S56 is executed a pluralityof times while the first driving frequency and the first shift time t3 iare changed. In a case where the first driving frequency is changed, thefirst average phase delay time also has a different value. That is,based on each of a plurality of combinations of the first average phasedelay time and the first shift time t3 ₁, the first zero cross pulse ZC1is output from the first zero cross pulse output portion 65A, and theirradiation is performed with the laser light from the light source 3.

In step S58, the third derivation portion 64 acquires the image dataobtained by the imaging performed by the imaging apparatus 7. Thedriving controller 5 and the imaging apparatus 7 are synchronized intime. Thus, the third derivation portion 64 can specify which image datais image data at a time of the irradiation with the laser light based onwhich combination of the first average phase delay time and the firstshift time t3 i, depending on time information provided in the imagedata.

In a case where the first shift time t3 i set as a temporary value forthe first average phase delay time is different from the actual firstshift time t3 i, the image indicated by the image data corresponding tothe combination of the first average phase delay time and the firstshift time t3 ₁ is as shown in FIG. 24 as an example. A bright point P1shown in FIG. 24 shows a bright point drawn on the surface to be scanned6 due to the reflection of the laser light of the irradiation from thelight source 3 by the mirror portion 20 of the MMD 4 based on the firstzero cross pulse ZC1 that depends on the point in time when the firstdriving signal becomes zero from a negative value toward a positivevalue. In addition, a bright point P2 shown in FIG. 24 shows a brightpoint drawn on the surface to be scanned 6 due to the reflection of thelaser light of the irradiation from the light source 3 by the mirrorportion 20 of the MMD 4 based on the first zero cross pulse ZC1 thatdepends on the point in time when the first driving signal becomes zerofrom a positive value toward a negative value.

That is, in this case, the bright point P1 and the bright point P2 areshifted on an axis corresponding to the second axis a₂ in the imageindicated by the image data. On the other hand, in a case where thefirst shift time t3 ₁ set as a temporary value for the first averagephase delay time matches the actual first shift time t3 ₁, the imageindicated by the image data corresponding to the combination of thefirst average phase delay time and the first shift time t3 ₁ is as shownin FIG. 25 as an example. That is, in this case, the bright point P1overlaps with the bright point P2.

Therefore, in step S60, the third derivation portion 64 specifies thecombination of the first average phase delay time and the first shifttime t3 ₁ at a time of capturing the image data in which the brightpoint P1 overlaps with the bright point P2 as a correct combination.Since a plurality of correct combinations are obtained, a relationshipbetween the first average phase delay time and the first shift time t3 ₁shown in FIG. 14 as an example is obtained. The third derivation portion64 derives the function f1 by approximating the obtained relationshipbetween the first average phase delay time and the first shift time t3i. The function f1 is used in step S14 of the first shift timederivation processing (see FIG. 18 ). The third derivation portion 64may store the obtained relationship between the first average phasedelay time and the first shift time t3 ₁ as a look-up table. In a casewhere the processing in step S60 is finished, the first calibrationprocessing is finished.

In step S70 in FIG. 26 , as described above, the second driving signalgeneration portion 60B generates the second driving signal and providesthe generated second driving signal to the pair of second actuators 32through the second phase shift portion 62B. That is, in the secondcalibration processing, the mirror portion 20 is caused to swing aroundonly the second axis a₂ and not swing around the first axis a₁.

In step S72, for each cycle, the second derivation portion 63B acquiresthe second phase delay time from the point in time when the seconddriving signal is zero to the point in time when the second angledetection signal S2 c is zero in the corresponding cycle. In step S74,the second derivation portion 63B derives the second average phase delaytime by averaging the second phase delay time in the most recentplurality of cycles acquired in step S72.

In step S76, the second zero cross pulse output portion 65B generatesthe second zero cross pulse ZC2 at the timing after the elapse of theadded time of the second average phase delay time and the second shifttime t3 ₂ from the timing at which the second driving signal crosseszero. The second zero cross pulse output portion 65B outputs thegenerated second zero cross pulse ZC2 to the light source drivingportion 66. In the second calibration processing, the light sourcedriving portion 66 performs irradiation with the laser light from thelight source 3 in synchronization with the second zero cross pulse ZC2.At this point, the second shift time t3 ₂ is a time set as a temporaryvalue.

The above processing from step S70 to step S76 is executed a pluralityof times while the second driving frequency and the second shift time t3₂ are changed. In a case where the second driving frequency is changed,the second average phase delay time also has a different value. That is,based on each of a plurality of combinations of the second average phasedelay time and the second shift time t3 ₂, the second zero cross pulseZC2 is output from the second zero cross pulse output portion 65B, andthe irradiation is performed with the laser light from the light source3.

In step S78, the third derivation portion 64 acquires the image dataobtained by the imaging performed by the imaging apparatus 7. Thedriving controller 5 and the imaging apparatus 7 are synchronized intime. Thus, the third derivation portion 64 can specify which image datais image data at a time of the irradiation with the laser light based onwhich combination of the second average phase delay time and the secondshift time t3 ₂, depending on the time information provided in the imagedata.

In a case where the second shift time t3 ₂ set as a temporary value forthe second average phase delay time is different from the actual secondshift time t3 ₂, the image indicated by the image data corresponding tothe combination of the second average phase delay time and the secondshift time t3 ₂ is as shown in FIG. 27 as an example. A bright point P3shown in FIG. 27 shows a bright point drawn on the surface to be scanned6 due to the reflection of the laser light of the irradiation from thelight source 3 by the mirror portion 20 of the MMD 4 based on the secondzero cross pulse ZC2 that depends on the point in time when the seconddriving signal becomes zero from a negative value toward a positivevalue. In addition, a bright point P4 shown in FIG. 27 shows a brightpoint drawn on the surface to be scanned 6 due to the reflection of thelaser light of the irradiation from the light source 3 by the mirrorportion 20 of the MMD 4 based on the second zero cross pulse ZC2 thatdepends on the point in time when the second driving signal becomes zerofrom a positive value toward a negative value.

That is, in this case, the bright point P3 and the bright point P4 areshifted on an axis corresponding to the first axis a₁ in the imageindicated by the image data. On the other hand, in a case where thesecond shift time t3 ₂ set as a temporary value for the second averagephase delay time matches the actual second shift time t3 ₂, the imageindicated by the image data corresponding to the combination of thesecond average phase delay time and the second shift time t3 ₂ is asshown in FIG. 28 as an example. That is, in this case, the bright pointP3 overlaps with the bright point P4.

Therefore, in step S80, the third derivation portion 64 specifies thecombination of the second average phase delay time and the second shifttime t3 ₂ at a time of capturing the image data in which the brightpoint P3 overlaps with the bright point P4 as a correct combination.Since a plurality of correct combinations are obtained, a relationshipbetween the second average phase delay time and the second shift time t3₂ shown in FIG. 15 as an example is obtained. The third derivationportion 64 derives the function f2 by approximating the obtainedrelationship between the second average phase delay time and the secondshift time t3 ₂. The function f2 is used in step S24 of the second shifttime derivation processing (see FIG. 19 ). The third derivation portion64 may store the obtained relationship between the second average phasedelay time and the second shift time t3 ₂ as a look-up table. In a casewhere the processing in step S70 is finished, the second calibrationprocessing is finished.

As described above, according to the present embodiment, shifts inoutput timing of the first zero cross pulse ZC1 and the second zerocross pulse ZC2 between each cycle can be reduced. Consequently, adecrease in image quality of the drawn image can be suppressed.

The configuration of the MMD 4 shown in the embodiment is an example.The configuration of the MMD 4 can be variously modified. For example,the first actuators 31 that cause the mirror portion 20 to swing aroundthe first axis a₁ may be arranged in the second movable frame 24, andthe second actuators 32 that cause the mirror portion 20 to swing aroundthe second axis a₂ may be arranged in the first movable frame 22.

In addition, in the embodiment, while a case where the pair of firstangle detection sensors 11A and 11B are arranged at positions that faceeach other with the first axis a₁ interposed therebetween is described,the present disclosure is not limited thereto. For example, as shown inFIG. 29 , the pair of first angle detection sensors 11A and 11B may bearranged at positions that face each other with the second axis a₂interposed therebetween. In the example in FIG. 29 , each of the pair offirst angle detection sensors 11A and 11B is arranged near the firstsupport portions 21 on the first movable frame 22. The first angledetection sensor 11A is arranged near the first support portion 21connected to one side of the mirror portion 20. The first angledetection sensor 11B is arranged near the first support portion 21connected to the other side of the mirror portion 20. Accordingly, thepair of first angle detection sensors 11A and 11B are arranged atpositions that face each other with the second axis a₂ interposedtherebetween and face each other with the mirror portion 20 interposedtherebetween. In addition, the pair of first angle detection sensors 11Aand 11B are arranged at positions that are shifted in the same direction(in the example in FIG. 29 , the −X direction) from the first axis a₁.

As in the embodiment, in a case where the pair of first angle detectionsensors 11A and 11B are arranged at positions that face each other withthe first axis a₁ interposed therebetween, the vibration noise can beremoved by subtracting one of the output signals of both of the firstangle detection sensors 11A and 11B from the other. On the other hand,as in this form example, in a case where the pair of first angledetection sensors 11A and 11B are arranged at positions that face eachother with the second axis a₂ interposed therebetween, the vibrationnoise can be removed by adding the output signals of both of the firstangle detection sensors 11A and 11B.

An example of a configuration of the first signal processing portion 61Ain this form example is shown in FIG. 30 . As shown in FIG. 30 , in thisform example, the first signal processing portion 61A includes anaddition circuit 73A instead of the subtraction circuit 73. The additioncircuit 73A outputs a value obtained by adding the signal S1 b ₁ inputfrom the first angle detection sensor 11A through the buffer amplifier71 to the signal S1 b ₂ input from the first angle detection sensor 11Bthrough the variable gain amplifier 72.

In addition, in the embodiment, while a case where the pair of secondangle detection sensors 12A and 12B are arranged at positions that faceeach other with the second axis a₂ interposed therebetween is described,the present disclosure is not limited thereto. For example, as shown inFIG. 29 , the pair of second angle detection sensors 12A and 12B may bearranged at positions that face each other with the first axis a₁interposed therebetween. In the example in FIG. 29 , each of the pair ofsecond angle detection sensors 12A and 12B is arranged near the secondsupport portions 23 on the second movable frame 24. The second angledetection sensor 12A is arranged near the second support portion 23connected to one side of the first movable frame 22. The second angledetection sensor 12B is arranged near the second support portion 23connected to the other side of the first movable frame 22. Accordingly,the pair of second angle detection sensors 12A and 12B are arranged atpositions that face each other with the first axis a₁ interposedtherebetween and face each other with the mirror portion 20 and thefirst movable frame 22 interposed therebetween. In addition, the pair ofsecond angle detection sensors 12A and 12B are arranged at positionsthat are shifted in the same direction (in the example in FIG. 29 , the+Y direction) from the second axis a₂.

As in the embodiment, in a case where the pair of second angle detectionsensors 12A and 12B are arranged at positions that face each other withthe second axis a₂ interposed therebetween, the vibration noise can beremoved by subtracting one of the output signals of both of the secondangle detection sensors 12A and 12B from the other. On the other hand,as in this form example, in a case where the pair of second angledetection sensors 12A and 12B are arranged at positions that face eachother with the first axis a₁ interposed therebetween, the vibrationnoise can be removed by adding the output signals of both of the secondangle detection sensors 12A and 12B. A configuration of the secondsignal processing portion 61B in this form example can be implemented bythe same configuration as the first signal processing portion 61A shownin FIG. 30 and thus, will not be described.

In addition, in the embodiment, a form of providing any one of the pairof first angle detection sensors 11A and 11B in the MMD 4 may beapplied. Similarly, a form of providing any one of the pair of secondangle detection sensors 12A and 12B in the MMD 4 may be applied.

In addition, in the embodiment, while a case of deriving the firstaverage phase delay time and the second average phase delay time at atime of drawing the image is described, the present disclosure is notlimited thereto. A form of acquiring the first average phase delay timeand the second average phase delay time by executing an average phasedelay time derivation mode in which the first average phase delay timeand the second average phase delay time are derived in the calibrationmay be applied. In this case, the first average phase delay time and thesecond average phase delay time acquired in advance in the calibrationare used in the generation of the first zero cross pulse ZC1 and thesecond zero cross pulse ZC2. Examples of the execution timing of thecalibration in this case include when the MMD 4 is started, and thetiming at which the instruction to execute the calibration is input bythe user.

In addition, in the embodiment, while a case where the third derivationportion 64 derives the first shift time t3 i corresponding to the firstaverage phase delay time in accordance with the function f1 isdescribed, the present disclosure is not limited thereto. FIG. 31 showsan example of a relationship between the first driving frequency and thefirst shift time t3 i. In FIG. 31 , the relationship between the firstdriving frequency and the first shift time t3 i in a case where themirror portion 20 is caused to swing around the first axis a₁ by each oftwo different first deflection angles θ₁ is shown. In addition, a solidline in FIG. 31 shows the relationship between the first drivingfrequency and the first shift time t3 i in a state where the mirrorportion 20 is caused to swing around the first axis a₁ by a larger angleof the first deflection angle θ₁ than a broken line. As shown in FIG. 31, as the first driving frequency is increased, the first shift time 31is increased. In FIG. 31 , while the relationship between the firstdriving frequency and the first shift time t3 i is shown, the firstshift time t3 i changes in accordance with not only the first drivingfrequency but also a driving voltage of the first driving signal. Forexample, the driving voltage of the first driving signal corresponds toan amplitude of the first driving signal.

Therefore, the third derivation portion 64 may further derive the firstshift time t3 i corresponding to a first driving frequency F1 and adriving voltage V1 of the first driving signal in accordance with afunction f3 shown as follows.

t3₁ =f3(t1_(avg) ,F1,V1)

Similarly, the third derivation portion 64 may further derive the secondshift time t3 ₂ corresponding to a second driving frequency F2 and adriving voltage V2 of the second driving signal in accordance with afunction f4 shown as follows.

t3₂ =f4(t2_(avg) ,F2,V2)

In addition, the third derivation portion 64 may further derive thefirst shift time t3 ₁ and the second shift time t3 ₂ corresponding to anambient temperature T in accordance with functions f5 and f6 shown asfollows. In this case, a temperature sensor that measures the ambienttemperature is provided in the MMD 4.

t3₁ =f5(t1_(avg) ,T)

t3₂ =f6(t2_(avg) ,T)

In addition, the third derivation portion 64 may further derive thefirst shift time t3 i corresponding to the first driving frequency F1,the driving voltage V1 of the first driving signal, and the ambienttemperature T in accordance with a function f7 shown as follows.

t3₁ =f7(t1_(avg) ,F1,V1,T)

Similarly, the third derivation portion 64 may further derive the secondshift time t3 ₂ corresponding to the second driving frequency F2, thedriving voltage V2 of the second driving signal, and the ambienttemperature T in accordance with a function f8 shown as follows.

t3₂ =f8(t2_(avg) ,F2,V2,T)

In the functions f3 and f7, only one of the first driving frequency F1and the driving voltage V1 of the first driving signal may be used. Inaddition, in the functions f4 and f8, only one of the second drivingfrequency F2 and the driving voltage V2 of the second driving signal maybe used.

In addition, a hardware configuration of the driving controller 5 can bevariously modified. The driving controller 5 can be configured using atleast one of an analog operation circuit or a digital operation circuit.The driving controller 5 may be configured with one processor or may beconfigured with a combination of two or more processors of the same typeor different types. Examples of the processor include a centralprocessing unit (CPU), a programmable logic device (PLD), and adedicated electric circuit. As is well known, the CPU is ageneral-purpose processor that executes software (program) to functionas various processing portions. The PLD is a processor such as a fieldprogrammable gate array (FPGA) that has a circuit configurationchangeable after manufacturing. The dedicated electric circuit is aprocessor such as an application specific integrated circuit (ASIC) thathas a circuit configuration dedicatedly designed to perform specificprocessing.

What is claimed is:
 1. An optical scanning device comprising: a mirrorportion that has a reflecting surface on which an incidence ray isreflected; a first actuator that causes the mirror portion to swingaround a first axis which is in a plane including the reflecting surfaceat a time of a standstill of the mirror portion; a second actuator thatcauses the mirror portion to swing around a second axis which is in theplane including the reflecting surface at the time of the standstill ofthe mirror portion and intersects with the first axis; a first angledetection sensor that outputs a signal corresponding to an angle of themirror portion around the first axis; a second angle detection sensorthat outputs a signal corresponding to an angle of the mirror portionaround the second axis; and at least one processor, wherein theprocessor is configured to provide a first driving signal having a firstdriving frequency to the first actuator, provide a second driving signalhaving a second driving frequency to the second actuator, derive a firstaverage phase delay time by averaging a first phase delay time of theoutput signal of the first angle detection sensor with respect to thefirst driving signal in a plurality of cycles, derive a second averagephase delay time by averaging a second phase delay time of the outputsignal of the second angle detection sensor with respect to the seconddriving signal in a plurality of cycles, generate a first referencesignal representing that the angle around the first axis is equal to areference angle based on the first driving signal and the first averagephase delay time, and generate a second reference signal representingthat the angle around the second axis is equal to a reference anglebased on the second driving signal and the second average phase delaytime.
 2. The optical scanning device according to claim 1, wherein thefirst angle detection sensor includes a pair of angle detection sensorsarranged at positions that face each other with the first axis or thesecond axis interposed between the positions, the output signal of thefirst angle detection sensor is an output signal obtained by adding orsubtracting a pair of output signals output from the pair of angledetection sensors, the second angle detection sensor includes a pair ofangle detection sensors arranged at positions that face each other withthe first axis or the second axis interposed between the positions, andthe output signal of the second angle detection sensor is an outputsignal obtained by adding or subtracting a pair of output signals outputfrom the pair of angle detection sensors.
 3. The optical scanning deviceaccording to claim 1, wherein the first reference signal is a signalrepresenting that the angle around the first axis is zero, and thesecond reference signal is a signal representing that the angle aroundthe second axis is zero.
 4. The optical scanning device according toclaim 3, wherein the processor is configured to derive the first averagephase delay time by averaging the first phase delay time at a point intime when the output signal of the first angle detection sensor is zero,and derive the second average phase delay time by averaging the secondphase delay time at a point in time when the output signal of the secondangle detection sensor is zero.
 5. The optical scanning device accordingto claim 4, wherein the processor is configured to derive the firstaverage phase delay time by averaging the first phase delay time from apoint in time when the first driving signal is zero to the point in timewhen the output signal of the first angle detection sensor is zero in acorresponding cycle, and derive the second average phase delay time byaveraging the second phase delay time from a point in time when thesecond driving signal is zero to the point in time when the outputsignal of the second angle detection sensor is zero in a correspondingcycle.
 6. The optical scanning device according to claim 1, wherein theprocessor is configured to generate each of the first reference signaland the second reference signal based on a time obtained by adding ashift time corresponding to a preset condition to each of the firstaverage phase delay time and the second average phase delay time.
 7. Theoptical scanning device according to claim 6, wherein the conditionincludes the first phase delay time and the second phase delay time. 8.The optical scanning device according to claim 7, wherein the conditionfurther includes a driving voltage of the first driving signal and adriving voltage of the second driving signal.
 9. The optical scanningdevice according to claim 7, wherein the condition further includes thefirst driving frequency and the second driving frequency.
 10. Theoptical scanning device according to claim 7, wherein the conditionfurther includes an ambient temperature.
 11. The optical scanning deviceaccording to claim 6, wherein a shift time derivation mode in which theshift time is derived is provided, and the processor is configured toacquire the shift time by executing the shift time derivation mode incalibration, and use the shift time acquired in advance in thecalibration in generating the first reference signal and the secondreference signal.
 12. The optical scanning device according to claim 1,wherein an average phase delay time derivation mode in which the firstaverage phase delay time and the second average phase delay time arederived is provided, and the processor is configured to acquire thefirst average phase delay time and the second average phase delay timeby executing the average phase delay time derivation mode incalibration, and use the first average phase delay time and the secondaverage phase delay time acquired in advance in the calibration ingenerating the first reference signal and the second reference signal.13. An image drawing system comprising: the optical scanning deviceaccording to claim 1; and a light source that irradiates the mirrorportion with light, wherein the processor is configured to control anirradiation timing of the light of the light source based on the firstreference signal and the second reference signal.
 14. A driving methodof an optical scanning device including a mirror portion that has areflecting surface on which an incidence ray is reflected, a firstactuator that causes the mirror portion to swing around a first axiswhich is in a plane including the reflecting surface at a time of astandstill of the mirror portion, a second actuator that causes themirror portion to swing around a second axis which is in the planeincluding the reflecting surface at the time of the standstill of themirror portion and intersects with the first axis, a first angledetection sensor that outputs a signal corresponding to an angle of themirror portion around the first axis, and a second angle detectionsensor that outputs a signal corresponding to an angle of the mirrorportion around the second axis, the driving method comprising: providinga first driving signal having a first driving frequency to the firstactuator; providing a second driving signal having a second drivingfrequency to the second actuator; deriving a first average phase delaytime by averaging a first phase delay time of the output signal of thefirst angle detection sensor with respect to the first driving signal ina plurality of cycles; deriving a second average phase delay time byaveraging a second phase delay time of the output signal of the secondangle detection sensor with respect to the second driving signal in aplurality of cycles; generating a first reference signal representingthat the angle around the first axis is equal to a reference angle basedon the first driving signal and the first average phase delay time; andgenerating a second reference signal representing that the angle aroundthe second axis is equal to a reference angle based on the seconddriving signal and the second average phase delay time.